OMAPFB: move dssdev->sync call out from omapfb_realloc_fbmem

Currently omapfb_realloc_fbmem() calls dssdev->sync to ensure any
possible frame update is finished. This patch moves the call to
dssdev->sync from omapfb_realloc_fbmem to the callers of
omapfb_realloc_fbmem.

This keeps dssdev related calls out from omapfb_realloc_fbmem, which
makes sense as the function should only deal with fb memory. Also, this
seems to avoid a lockdep warning about possible circular locking.
However, the exact reason for that warning is still unclear.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>